The present invention relates to the field of measuring departures from planeness in the surfaces of road and highway pavements, and of all paths on which vehicles of any type travel, including runways.
Departures from planeness in road or highway pavements, in traffic paths of all types, and in runways, give rise to significant drawbacks for users and also for the works themselves. For users, numerous studies have shown that the comfort, safety, and costs of using vehicles are influenced to a very great extent by the vibrations induced by departures from planeness. So far as the works themselves are concerned, these defects give rise to additional stresses which shorten their lifetime.
As a result, regulations require minimum quality standards to be satisfied when the works are constructed, both for satisfying users and for ensuring long life for the work. An evaluation of the planeness qualities of a work is also one of the major parameters used during periodic inspections thereof for maintenance purposes.
The advantage of having means for measuring departures from planeness is therefore manifest, both for contractors and for authorities.
In conventional road terminology, it is the practice to use the terms xe2x80x9cprofilexe2x80x9d and xe2x80x9cdepartures from profilexe2x80x9d rather than xe2x80x9cdepartures from planenessxe2x80x9d, and apparatus capable of providing an image of the real profile of the road surface by sampling along one or more substantially parallel lines in a given direction, and capable of being included in ordinary traffic, is referred to as a xe2x80x9cdynamicxe2x80x9d profilometer, as contrasted with xe2x80x9cstaticxe2x80x9d profilometers which require the road under test to be closed to traffic.
It should be observed that all existing profilometers give an image that approximates to the real profile, firstly because they do not observe the entire surface but only a finite number of lines, and secondly because they filter the real profile, deforming it both in amplitude and in phase within wavelength bands where their response differs from unity, and generally in phase even in frequency bands where their amplitude response is indeed unity.
So far as roads are concerned, the following are generally distinguished:
microtexture for wavelengths shorter than 0.5 millimeters (mm);
macrotexture for wavelengths lying in the range 0.5 mm to 50 mm;
megatexture for wavelengths lying in the range 50 mm to 0.5 meters (m); and
smoothness (or conversely roughness) for wavelengths lying in the range 0.5 m to 50 m.
Present dynamic profilometers can be classified in two broad categories:
profilometers using an inertial reference making use of an inertial type artificial horizon as a reference plane, and measuring variations in height relative to said reference plane in order to estimate profile; by construction such devices are sensitive to measurement speed and to the quality of their reference plane; and
profilometers using a pure geometrical reference, which starting from a known position enable profile to be reconstructed by moving a ruler with precision; by construction, these devices are sensitive to the precision with which the ruler is moved and also to measurement errors, where the influence of such errors generally increases exponentially with distance.
The state of the art is illustrated by document WO 98/24977 published on Jun. 11, 1998 which shows a profilometer on board a vehicle, the profilometer having three contactless distance-measuring sensors mounted at the front of the vehicle chassis and aligned transversely in a direction perpendicular to the travel direction of the vehicle, together with a system for measuring the positions of the sensors relative to an artificial horizon, said system comprising in particular an accelerometer for measuring vertical acceleration and inclinometers for measuring the inclinations of the chassis relative to the artificial horizon, both in terms of roll and in terms of pitch. Each sensor provides a measurement of its height above the pavement. By using a computer that is connected to the various devices, that profilometer makes it possible to reconstruct the profile along three lines drawn along the pavement, one line to the right of the vehicle, one line to the left of the vehicle, and a central line.
U.S. Pat. No. 4,571,695 describes a device whose intended purpose is to measure the smoothness of a pavement, i.e. its deformation in the absence of any load relative to an ideal surface, and it also seeks to measure pavement deflection, i.e. deformation under the effect of a load relative to its state in the absence of load.
Given the principle on which it works, the device described in U.S. Pat. No. 4,571,695 requires four sensors referenced 10, 20, 30, and 40 in its FIGS. 1 and 2. That document describes measuring smoothness with the help of a memory system, requiring extreme accuracy in the positioning of one measurement relative to another. The term xe2x80x9cmemory systemxe2x80x9d is used to designate a measurement system in which the value of measurement n depends on the value of measurement k where k less than n. Such systems present at least two particular features: firstly, any error in measurement k induces an error in measurement n and entrains error propagation, and secondly it is generally necessary to make assumptions about the first measurement or to apply a posteriori corrections on the set of measurements, even if they do not include any error, in order to compensate for the lack of any antecedents for the first measurement. Thus, in the measurement method described in U.S. Pat. No. 4,571,695, the height of each measurement point is a function of previously measured points and the pitch at which measurement points are sampled is determined by the relative position of the various sensors along the beam which they use as a support.
The present invention thus seeks to provide a method of reconstituting the profile of a line drawn on a pavement that makes it possible to ignore the oscillations of the support for the measuring devices (body movements if the support is a road vehicle), variations in speed, speeds of the support, and problems of phase, of the influence of the shape of support beam on the sampling pitch, and of the need to use the preceding points in order to calculate the current point.
The method of the invention is characterized by:
moving over the pavement three contactless distance-measuring sensors that are equidistantly in horizontal alignment in the direction of motion;
simultaneously measuring the height of each of the three sensors above the pavement;
measuring the distance travelled by one of said sensors; and
substracting twice the height measured by the middle sensor from the sum of the heights measured by the end sensors.
It can be shown by calculation that the result of the subtraction is proportional to the function that represents the profile, and that it is independent of the position of the artificial horizon used in conventional methods of calculation. This is shown below in the present specification. In addition, the coefficient of proportionality does not include a phase term. As a result, if a direct Fourier transform is applied to the signal representative of the result of the subtraction, and if a simple multiplying coefficient is applied to the real and imaginary portions of the transform, then the initial profile can be obtained by performing the inverse Fourier transform.
The three contactless measurement sensors preferably pick up the distance between themselves and the pavement simultaneously. This operation is repeated each time the sensors have travelled through a selected distance. This distance is fixed for any one series of measurements.
The travel distance pitch is fixed for a series of measurements corresponding to a sample or to a portion of the pavement, but this travel distance pitch can be modified at will. It can be made longer when it is desired to measure the smoothness or the megastructure of the pavement, or shorter when it is desired to measure the microtexture or the macrotexture of certain lengths of the pavement.
The contactless distance-measuring sensors are preferably of the laser type using a triangulation principle or a method based on defocusing, as explained in EP 0 278 269. It is also possible to envisage using ultrasound sensors operating at high frequency or conventional telemetry devices of precision enabling resolution of about 10 microns to be obtained.
The invention also provides apparatus for implementing the method.
The apparatus is characterized by the fact that it comprises:
a carrying vehicle suitable for being moved along the pavement;
a longitudinal beam carried by said vehicle in such a manner as to be substantially horizontal;
three contactless distance-measuring sensors that are mounted equidistantly in horizontal alignment on said beam and that are suitable for delivering signals representative of their heights above the pavement;
a device for measuring the distance travelled by the vehicle; and
a computer receiving signals from the device for measuring the distance travelled by the vehicle and from the contactless distance-measuring sensors.
Because of the principle on which calculation is based, the proposed apparatus does not introduce any phase distortion in profile measurement. As a result it enables the true profile to be reconstituted easily by using simple signal processing methods.
The proposed apparatus does not use an inertial reference. It can thus easily be used in traffic at varying speed, e.g. in an urban area, without that affecting the result of the measurements taken.
The proposed apparatus is not of the type having a pure geometrical reference. It is thus less sensitive to measurement errors and less demanding concerning the quality of the distance reference used.
Since the proposed apparatus uses contactless sensors and delivers results that are independent of the movements of its carrying apparatus, it can be used during the operations of building the structures mentioned in the introduction.
The proposed apparatus is equally suitable for dynamically measuring smoothness and megatexture, or alternatively statically measuring microtexture and macrotexture.
It should be observed that the carrying vehicle can be the chassis of a conventional road vehicle.